Face detection methods have become very well established within digital cameras in recent years. This technology brings a range of benefits including enhanced acquisition of the main image and adaptation of the acquisition process to optimized image appearance and quality based on the detected faces.
More recently, newer consumer cameras have begun to feature wide field of view (WFOV) imaging systems and as the benefits of obtaining a wider scene become apparent to consumers, it is expected that further growth will ensue in such imaging systems along with an ability to achieve even wider fields of view over time. In professional cameras, such WFOV imaging systems are better known, the most well known being the fish-eye lens. WFOV imaging systems are also used in a range of applications including Google's “street-view” technology and for some video-phone systems where they enable a number of people sitting at a table to be imaged by a single sensor and optical system.
Now mapping a WFOV image onto a rectilinear image sensor is non-trivial and a wide range of different techniques are available depending on the exact form of the WFOV lens and associated optical elements. The desired image perspective is also important.
Unfortunately due to the complexity of WFOV imaging systems the benefits of face detection technologies have not been successfully applied to such systems. In particular, faces near the center of a WFOV camera appear closer to the camera and experience some geometrical distortions. Faces about mid-way from the center appear at approximately the correct distances from the camera and experience less significant distortions. Faces towards the edge experience very significant geometrical distortions. The exact nature of each of these types of perspective and geometrical distortion depend on the nature of the lens and optical system.
Clearly a conventional face detection or face tracking system employing rectangular classifiers or integral image techniques cannot be conveniently applied directly to such faces. Accordingly methods are desired to adapt and compensate for image distortions within such WFOV imaging systems so that face detection technologies can be successfully employed in devices like digital cameras and video phone systems.
The following is from http://www.panorama-numerique.com/squeeze/squeeze.htm, where it is referred to as “Correcting wider than 90° rectilinear images to print or to display architecture panoramas,” by Georges Lagarde. The indicated point is to remove stretching near the sides of a wide angle shot. Mr. Lagarde indicates that one simply has to “just squeeze your panos!” However, in practice, there are greater complexities that than. This application provides several embodiments after this introduction for displaying panoramas without all the inherent distortion.
Mr. Lagarde points out that 180° panoramic images require large screen real-estate. Reduced to a more usual size, Mr. Lagarde presents the examples illustrated at FIGS. 1A-1G. While panoramic images are typically difficult to appraise, displaying them in a narrow window has generally been avoided, and instead a 1280×1024 screen or “larger” and a fast Internet connection may be typically recommended.
Mr. Lagarde points out that the exact same source images of FIGS. 1A-1G (showing the Préfecture building in Grenoble, France) were used in a previous tutorial: Rectilinear/cylindric/equirectangular selection made easy, and that different but acceptable panoramic images can result from stitching the same source images and then using different projection modes is implied here and there.
FIG. 1A illustrates Piazza Navona, Roma by Gaspar Van Wittel, 1652-1736 (Museo Thyssen-Bornemisza, Madrid).
Mr. Lagarde indicates that most photographers restrict themselves to subjects which can be photographed with a rectilinear lens (plane projection). A small number of them sometimes use a fisheye lens (spherical projection) or a rotating lens camera (cylindrical projection) or a computer (stitcher programs make use of various projection modes), but when the field of view (horizontal FOV and/or vertical FOV) is higher than 90 degrees (or about, this actually depends on the subject) they are disturbed by the “excessive wide-angle distortion” found in the resulting images.
Adapting the usual projection modes to the subject and/or using multiple local projections to avoid this distortion is a violation of the classical perspective rules, but escaping classical perspective rules is exactly what sketchers and painters always did to avoid unpleasant images. Mr. Lagarde points out that this was explained by Anton Maria Zanetti and Antonio Conti using the words of their times (“Il Professore m'entendara”) when they described how the camera ottica was used by the seventeenth century Venetian masters. Because the field of view of the lenses available then was much lower than 90°, that a camera oscura was not able to display the very wide vedute they sketched and painted is evident: the solution was to record several images and to stitch them onto the canvas to get a single view (strangely enough, that the field of view is limited to about 90 degrees when one uses classical perspective—aka rectilinear projection on a vertical plane—is not handled in most perspective treatises.)
Equivalent “tricks” can be used for photographic images:                Use of several projection planes—their number and location depending of the subject—for a single resulting image. This is the method explained by L. Zelnik-Manor in Squaring the Circle in Panoramas (see references.)        Use of several projection modes—the selected modes depending of the subject—for a single resulting image. This is the method proposed by Buho (Eric S.) and used by Johnh (John Houghton) in Hybrid Rectilinear & Cylindrical projections (see references.)        Use of an “altered rectilinear” projection (thus no more rectilinear) where the modification is a varying horizontal compression, null in the center, high near the sides). This is the method proposed by Olivier_G (Olivier Gallen) in Panoramas: la perspective classique ne s'applique plus! (see references.)        Use of “squeezed rectilinear” projection (neither an actual rectilinear one) where the modification is a varying horizontal and vertical compression, null near the horizon (shown as a red line in the examples), null near a vertical line which goes through to the main vanishing point (shown as a blue line in the examples), increasing like tangent (angle) toward the sides (where angle correspond to the angular distance between the point and the line.)        
If photographers like the results, no doubt they will use that.